EV is a very confusing something! In this thread Metza gave a really nice explanation on how EV is calculated in a hand. (Nice one Metza! I don't dare to take on that challenge!)

Also:
The EV line in you graph is AI EV. This means that if you aren't AI in a that goes to SD the EV line will just follow your green line. So when you have a session without AI's that go to showdown you wouldn't even be able to see your EV line.
When you are AI and it goes to showdown then the EV line will take a different route then your green line.